NBC News' Richard Engel talks to Gianluigi Nuzzi, one of Italy's top investigative journalists, about the resignation of Pope Benedict XVI. Nuzzi's interviews with Benedict's whistleblower butler led to the Vatileaks scandal. Nuzzi and others allege that within the Vatican there were financial cover-ups and a twisted web of money, power and sex.

Tracy Connor, Staff Writer, NBC News

As the Vatican waits for a new pope under a cloud of scandal, the journalist at the center of the Vatileaks case is revealing the high-stakes, cloak-and-dagger operation he undertook to protect the butler who went public with the secrets.

Investigative journalist Gianluigi Nuzzi told NBC News' Richard Engel how he met Paolo Gabriele in public squares and used old-fashioned public phones to set up rendezvous to make it harder for anyone to eavesdrop on their blockbuster conversations.

He gave Gabriele a code name -- Maria -- and would leave it on the door buzzer he was to press for meetings in a Rome apartment, Nuzzi said in a "Rock Center with Brian Williams" interview.

"Then I understood why: because the Vatican has a very strong security system...Once Paolo Gabriele told me a confidence, which I do not know if it is true. He told me the cameras inside the Vatican as so powerful that they can even read the lips of people."

Their first sit-down, set up by intermediaries before Nuzzi even knew who he was meeting, was a "dangerous encounter," he said.

A dozen or so more followed, during which Gabriele gave Nuzzi photocopies of the pope's personal papers, including letters from a top aide, Monsignor Carlo Maria Viganò, who had investigated the alleged corruption. In one of the letters, Viganò complained that he felt he was being slandered and sidelined from the inside. He was eventually transferred off the case, and moved to Washington, D.C., to become Papal Nuncio, the Vatican’s diplomatic envoy.

Nuzzi used the documents for broadcast reports and a book that shed light on the infighting and dysfunction at the highest level of the church bureaucracy last year.

Gabriele, who said he was trying to help the pope and the church by shining a light on the dark underbelly of the Vatican, was eventually unmasked as the source of the leaks and sentenced to 18 months in Vatican custody. He was later pardoned by the pope and given a job in a hospital.

Pope Benedict XVI commissioned three retired and independent cardinals to investigate the leaks and they presented him with a report late last year, weeks before the pontiff shocked the world by announcing his abdication.

The Vatican has since denied reports that the cardinals' dossier contains details of a gay cabal in the Vatican and blackmail threats. Allegations of a gay Vatican subculture predate the Vatileaks scandal. In 2010, journalist Carlo Abbate went undercover and filmed Rome priests cavorting with other men.

Abbate doesn't buy the Vatican denials.

"In my opinion, Pope Benedict XVI's move represents his last attempt to save the Catholic Church from the public exposure of the contradictions of the church in the matter of sexuality," he said. "In a sense, he is casting himself aside in order to let those contradictions rise to the surface."

Benedict cited his age when he announced his resignation on Feb. 11 though he has also referred to the Vatican's difficulties. The 115 cardinals who will elect his successor have assembled in Rome but they will not see the Vatileaks report because Benedict decreed that only the next pontiff will get a copy.